This invention relates to a pilot valve for controlling a control valve in a main flow line, and more particularly to a fluid pressure boost attachment for the pilot valve.
Heretofore, such as illustrated in U.S. Pat. No. 3,572,359 dated Mar. 23, 1971, non-flowing pilot valves have been utilized to control a main valve in the main flow line for regulating a sensed or signal fluid pressure, either on the downstream side of the control valve or the upstream side of the control valve. The sensed fluid pressure being controlled is in fluid communication with a first fluid chamber in the pilot valve and in fluid communication with the flow line on one side of the control valve. A second fluid pressure chamber in the pilot valve is in fluid communication with the flow line on the other side of the control valve, and an intermediate fluid pressure chamber in the pilot valve is positioned between the first and second fluid pressure chambers. A spool valve member is movable between open and closed positions on valve seats separating the intermediate fluid chamber from the first and second fluid pressure chambers thereby controlling fluid flow between the chambers as desired under predetermined operating conditions.
Pilot valves are normally of two basic types, those that are adapted for use as pressure reducing valves to sense or control the downstream fluid pressure, or those adapted for use as a back pressure valve to sense or control the upstream fluid pressure. Aforementioned U.S. Pat. No. 3,572,359 shows embodiments for controlling or regulating both the upstream fluid pressure and the downstream fluid pressure.
It is noted that the response of the pilot valve is in response to a change in the pressure being sensed or controlled, and if for some reason such as a clogged filter, the fluid pressure being sensed or controlled is blocked in the line to the pilot valve, the control valve is not sufficiently responsive as the fluid pressure being sensed is inaccurate, and the control valve therefore receives an inaccurate pressure signal.